Technical Field
The present invention relates to an Al2O3-coated co-deposit, and an electrodeposition method for the manufacture thereof. More specifically, the present invention relates to an alloy substrate coated with a layer containing Ni, NiCrAlY, and Al2O3 and a method that uses a pulse electrodeposition solution technique.
Description of the Related Art
Metallic coatings, typically based on NiCrAlY or NiCoCrAlY constitution, are used as part of thermal barrier coatings (TBC) to provide environmental resistance to alloy substrates. The presence of Al in these compositions provides protective Al2O3 upon exposure to high temperature [See Padture, N., Gell, M., and Jordan, E., Science, 2002, vol. 296, p. 280 and Stott, E H. and Wood, G. C., Mater. Sci. Eng., Ser. A., 1987, p. 267, each incorporated herein by reference in their entirety]. It has been shown that the presence of a metallic coating promotes selective oxidation of Al thereby reducing the amount required to form Al2O3 [See Liu, Z., Gao, W., Dahm, K., and Wang, E, Acta Mater., 1998, vol. 46, p. 1691, incorporated herein by reference in its entirety]. The presence of Cr in the coating, in particular, contributes to selective oxidation of Al whereas Y serves to enhance scale adherence.
Al2O3-based coatings are important because alumina retards oxidation processes and provides protection to the underlying alloy during service [See Kofstad, P., High Temperature Corrosion, N.Y.: Elsevier Appl. Sci., 1988, incorporated herein by reference in its entirety]. Further, the presence of Al2O3 provides lowered oxidation rate and improved spallation resistance [See Liu, Z., Gao, W, and Li, M., Oxidation Met., 1998, vol. 51, p. 403, incorporated herein by reference in its entirety]. The protective nature of the Al2O3 is improved due to the presence of reactive elements such as Y, Y2O3, Hf, etc., which enhance scale adherence and reduce its grain size and growth rate [See Ul-Hamid, A., Oxidation Met., 2002, vol. 58, p. 23, incorporated herein by reference in its entirety]. The service life of the metallic coating depends on its composition and structure as well as on the composition of the underlying alloy substrate. In particular, the heat protection properties of the coatings are dependent on the amount of Al2O3 present on the surface.
Metallic coatings generally have a thickness ranging from 75 to 150 μm, and these coatings can be deposited using various techniques including plasma-spray, electron beam physical vapor deposition, magnetron sputter deposition, chemical vapor deposition, etc. However, these techniques have several drawbacks, including the need for a relatively elaborate setup and the expense required to carry out. Moreover, these processes are line of sight processes, and do not work well for complex and intricate shapes that include hidden surfaces.
Electrodeposition is a relatively easy and cost effective technique for coating substrates [See Saremi, M. and Bahraini, M., Trans. Inst. Met. Fin., 2003, vol. 81, p. 24; U.S. Pat. No. 5,824,205, 1998; and U.S. Pat. No. 5,833,829, 1998, each incorporated herein by reference in their entirety]. Electrodeposition is a non-line of sight process and can potentially be used to coat complex shapes and hidden surfaces. In addition, primary processing is carried out close to ambient temperatures allowing cost savings during the manufacturing process. Further, electrodeposition has the potential to be used as a repair technique for gas engine components resulting in cost reductions during maintenance and servicing [See U.S. Pat. No. 6,998,151, 2006, incorporated herein by reference in its entirety]. While pulse electrodeposition is expected to produce an overall smooth, dense and fine-grained coating structure [See Ul-Hamid, A., Dafalla, H., Quddus, A. et al., Appl. Surf. Sci., 2011, vol. 257, p. 9251, incorporated herein by reference in its entirety], previously published work on the synthesis of bond coats using this technique is limited [See Foster, J., Cameron, B. R, and Carew, J. A., Trans. Inst. Met. Finish, 1985, vol. 63, p. 115 and Zhou, Y., Peng, X., and Wang, E, Scripta Mater , 2004, vol. 50, p. 1429, each incorporated herein by reference in their entirety].
In view of the forgoing, the objective of the present disclosure is to provide an Al2O3-coated co-deposit that includes a superalloy substrate coated with NiCrAlY particles, Ni grains, and Al2O3, and a method of manufacturing the Al2O3-coated co-deposit using a pulse electrodeposition technique.